Learning Java

Chapter 4. The Java Language

In this chapter, we’ll introduce the framework of the Java language and some of its fundamental facilities. We’re not going to try to provide a full language reference here. Instead, we’ll lay out the basic structures of Java with special attention to how it differs from other languages. For example, we’ll take a close look at arrays in Java, because they are significantly different from those in some other languages. We won’t, on the other hand, spend much time explaining basic language constructs like loops and control structures. Nor will we talk much about Java’s object-oriented side here, as that’s covered in detail in Chapter 5 through Chapter 7.

As always, we’ll try to provide meaningful examples to illustrate how to use Java in everyday programming tasks.

Text Encoding

Java is a language for the Internet. Since the people of the Net speak and write in many different human languages, Java must be able to handle a large number of languages as well. One of the ways in which Java supports international access is through Unicode character encoding. Unicode uses a 16-bit character encoding; it’s a worldwide standard that supports the scripts (character sets) of most languages.^[12]

Java source code can be written using the Unicode character encoding and stored either in its full 16-bit form or with ASCII-encoded Unicode character values. This makes Java a friendly language for non-English-speaking programmers who can use their native alphabet for class, method, and variable names in Java code.

The Java char type and String objects also support Unicode. But if you’re concerned about having to labor with two-byte characters, you can relax. The String API makes the character encoding transparent to you. Unicode is also ASCII-friendly; the first 256 characters are defined to be identical to the first 256 characters in the ISO8859-1 (Latin-1) encoding; if you stick with these values, there’s really no distinction between the two.

Most platforms can’t display all currently defined Unicode characters. As a result, Java programs can be written with special Unicode escape sequences. A Unicode character can be represented with this escape sequence:

\uxxxx

xxxx is a sequence of one to four hexadecimal digits. The escape sequence indicates an ASCII-encoded Unicode character. This is also the form Java uses to output a Unicode character in an environment that doesn’t otherwise support them.

Java stores and manipulates characters and strings internally as Unicode values. Java also comes with classes to read and write Unicode-formatted character streams.

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^[12] For more information about Unicode, see http://www.unicode.org. Ironically, one of the scripts listed as “obsolete and archaic” and not currently supported by the Unicode standard is Javanese—a historical language of the people of the Island of Java.